Electron-tube stabilized amplifier



Sept. 12, 1961 B. H. TONGUE ELECTRON-TUBE STABILIZED AMPLIFIER Filed Aug. 15, 1959 2 LOAD INVENTOR BEN H TONGUE ATTORNEYS United States Patent O 2,999,985 ELECTRON-TUBE STABILIZED AMPLIFIER Ben H. Tongue, West Orange, NJ, asignorzto Blonder- Tongue Electronics, Newark, NJ., a eorporation of New Jersey Filed Aug. 13, 1959, Ser. No. 833,510

5 Claims. (Cl. 339-80) V The present invention relates to electron tube circuits and, more particularly, to radio-frequency circuits em bodying electron tubes having electrodes of the type that are disposed for shielding and relating purposes, beyond the active electron-flow path between the'main control grid and anode.

In my earlier United States Letters Patent, 2,790,036, issued April 23, 1957 for Electron-Tube Stabilized Amplifying Circuit, I disclose a technique for eliminating the deleterious detuning and bandwidth-variation effects that take place in pentode tubes and the like as the gain of the tube is varied. The present invention, on the other hand, relates to tubes embodying a cathode, control electrode and an anode as active elements, and shielding members disposed external to the active electron-flow path between the cathode, control electrode and anode. 'The invention is directed to solving the problem of'neutralizing the effects of capacitance that such external shielding members introduce into the operation of the tube, and simultaneously to eliminating bandwidth-variation efiects resulting from changes in radio-frequency loading and the like.

A further object is to provide a new and improved stabilized amplifying circuit.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims.

The invention will now be described in connection with the accompanying drawing, the single figure of which is a schematic circuit diagram illustrating the invention in preferred form.

An electron or vacuum tube 1 of the type previously described is shown in the drawing comprising an electronemissive cathode 2, a control or grid electrode 4, illustrated as surrounding the same, and a juxtaposed anode electrode 6. The active part of the electron tube is that portion in the vicinity of alignment and juxtaposition of the cathode 2, the central portion of the control electrode 4 and the central portion of the anode 6 within which electron flow occurs. External to the active electron-flow space and surrounding the laterally external regions 4' of the control-electrode grid 4, are channel-like shielding electrode configurations 8. While tubes of this character, such as the type 6ER5, have been found to provide improved signal-to-noise operation at high radio frequencies, they introduce, as a result of their construction, certain interelectro de capacities that make very difiicult the broadband neutralization of such tubes. It is with this problem that the present invention is primarily concerned.

As illustrated, the active electron-flow central region of the tube 1 will have the conventional control-grid-toplate capacitance, C There will also exist capacitance C between the laterally external regions 4 of the control grid 4 and the externally disposed channel electrode members 8. In addition, the externally disposed electrode members 8 will be capacitively coupled, as illustrated by the plurality of dotted capacitors C to the portions 6' of the anode electrode external to the central active-electronpath anode region 6. The operation of the channel electrodes 8 is, of course, clearly distinguishable from the function of screen-grid electrodes, as disclosed in my said prior Letters Patent, since the electrodes 8 draw no appreciable current and are customarily not connected with the plate supply source; but, on the century, are merely grounded to serve as external shielding elements. The members 8 are shown symmetrically disposed on each side of the active region of electron flow in the tube 1.

The cathode 2 is provided with a conventional cathode load R, by-passed by a capacitor C and connected to the bottom terminal of a source of radio-frequency or other alternating-current voltage, generalized by the box labelled Source. The 'upper terminal of the source is schematically shown connected by input-circuit conductor 12 to the control-grid electrode 4. The plate or anode 6 is similarly shown schematically connected to an outputcircuit load Zload which, in turn, connects through the B+, B- plate supply, back to the lower terminal of the source, shown grounded. The input and output circuits of the tube 1 are thus illustrated in generalized blockdiagram form since the present invention may be utilized with any desired type of radio-frequency or similar circuits, including well-know types of tuned radio-frequency input and output circuits. The term ground, moreover, as used in the specification and claims, is intended to embrace not only actual earthing, but, also, chassis or other reference potential as well. In order not to detract from the features of novelty, furthermore, the well-known details of the electrode bias supplies and other circuit refinements are not illustrated.

It has been discovered that the selection of an appropriate rather critical value of inductance L in the connection from the external electrode 8 to the ground terminal B can eliminate the deleterious efiects of feedback between the output'and input circuits through the interelectrode capacitance C in the active region of the tube electron flow; and this despite the fact that, unlike conventional screen-grid electrodes and the like, discussed in my prior Letters Patent, the electrode 8 is disposed external to such active region. In accordance with the invention, if L is adjusted to a value suflicient, at the predetermined desired frequency, to introduce a phase shift of substantially one-hundred eighty degrees into the radio frequency currents coupled in the region external to the said active electron-flow region of the tube, namely, between capacitances C (from the external anode regions 6 and the electrode 8) and C (from the external grid regions 4' and the electrode 8), with respect to the phase of energy fed back in the active electron-flow region be tween the central regions of the anode 6 and control electrode 4 at C substantially zero net feedback current flows from the output to the input circuit. The reactance of L at the desired frequency, moreover, is Smaller than that of either of the capacitances C or C external to the active electron-flow path.

Further modifications Will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. An electron-tube circuit for operation at a predetermined radio frequency having, in combination, an electron tube provided with an anode, a grounded cathode and a control electrode forming an active region in the tube for the flow of electrons therebetween, and a further electrode within the tube extending external to the said active region and capacitively coupled to portions of the said anode and control electrode also extending external to the said active region, radio-frequency input and output circuits connected from the cathode to the control electrode and to the anode, respectively, and a circuit connection from the said further electrode to ground having an impedance therein of sufiicient reactance at the said predetermined radio-frequency to shift the phase of the radiofrequeucy energy fed from the said output circuit to the said input circuit through said capacitive coupling from the said external portions of the anode and control electrode to the further electrode substantially one hundred eighty degrees with respect to the phase of the radiofrequency energy fed from the said output circuit to the said input circuit through the inherent anode-to-control electrode capacitance in the said active region of electron flow. 1

2. An electron-tube circuit as claimed inlclaim '1 and in which the said further electrode envelopes the said portions of the control electrode external to the said active region. i

3. An electron-tube circuit as claimed in claim 2 and in which the said external portions of each of the anode, control electrode and further electrode are substantially symmetrically disposed on each side of the said active region of electron flow in the tube.

4. An electron-tube circuit for operation at a predeter mined radio frequency having, in combination, an electron tube provided with an anode, a grounded cathode and a control electrode forming an active region in the tube for the flow of electrons therebetween, and a further electrode Within the tube extending external to the said active region and capacitively coupled to portions of the said anode and control electrode also extending external to the said active region, radio-frequency input and output circuits connected from the cathode to the control electrode and to the anode, respectively, and a circuit connection from the said further electrode to ground having an inductance therein of sufficient reactance at the said predetermined radio-frequency to shift the phase of the radio-frequency energy fed from the said output circuit to the said input circuit through said capacitive coupling from the said ex-' ternal portions of the anode and control electrode to the further electrode substantially one hundred eighty degrees a a 4 through the inherent anode-to-control electrode capacitance in thesaid active region of electron flow.

5. An electron-tube circuit for operation at a predetermined radio frequency having, in combination, an electron tube provided with an anode, a grounded cathode and a control electrode'iorming an active region in the tube for thefloiv-of electrons therebetwe'en, and a further electrode within the tube extending external to the said active regio'n and capacitivc'ly coupled to portions of the said anode and control electrode also extending external to the said active "region, radio-frequency input and output circuits connected from the cathode to the control electrode and to the anode, respectively, and a circuit connection from the said further electrode to ground having an inductance therein'of suificient reactance at the said predetermined radio-frequency to shift 'the'phase of the radio- ,frequency energy fed from the said output circuit to the said input circuit through said capacitive coupling from the said external portions of the anode and control electrode capacitance in the said active region of electron from the said output circuit to the said input circuit flow, the said inductance having a reactance value, however, less than that of the said capacitive coupling between the said extemal portions of the anode and control electrode and the further electrode at the said predetermined 1 radio frequency.

References Cited in the file of this patent UNITED STATES PATENTS 2,254,095 Thompson Aug. 26, 1941 2,442,576 7 Alma June 1, 1948 2,790,036 Tongue Apr. 23, 1957 

